When a reddish brown metal X comes in contact with air and moisture, it forms a green covering of metal carbonate over the metal X. What is X?
Copper
When reddish brown metal copper comes in contact with air and moisture, it gets covered with a green layer of basic copper carbonate in the presence of CO2 and moisture.
2Cu+O2+CO2+H2O→CuCO3.Cu(OH)2